Dynamical effects of small-scale gravity waves of lower atmospheric origin on the equinoctial thermosphere

Details Dynamical effects of small-scale gravity waves of lower atmospheric origin on the equinoctial thermosphere Dynamical effects of small-scale gravity waves of lower atmospheric origin on the equinoctial thermosphere

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa31b1969y&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SA31B-1969

Physics

[0358] Atmospheric Composition And Structure / Thermosphere: Energy Deposition, [3319] Atmospheric Processes / General Circulation, [3384] Atmospheric Processes / Acoustic-Gravity Waves, [3365] Atmospheric Processes / Subgrid-Scale Parameterization

Scientific paper

Small-scale internal gravity waves (GWs) propagating directly from the lower to upper atmosphere play a significant dynamical role for the general circulation of the thermosphere at solstice (Yigit et al., 2009). Using the extended spectral nonlinear gravity wave parameterization of Yigit et al. (2008) implemented into a 3-D coupled general circulation model, this work investigates the effects of a broad spectrum of small-scale GWs of lower atmospheric origin on the equinoctial thermosphere for the first time. GWs propagate to F region altitudes in both hemispheres, producing appreciable drag on the mean zonal wind. A modification of the two-cell equinoctial mean circulation by GWs is simulated. The mean zonal GW drag is comparable to the ion drag up to the middle thermosphere. While the mean dynamical effects of GWs is the deceleration of the mean flow, the instantaneous GW body force can have both signs. In the Southern Hemisphere high-latitude, GWs produce very large torque, the mechanism of which is investigated in detail. GW anisotropy plays a crucial role in offsetting and modulating wave filtering, introducing increased favorable propagation conditions for westerly harmonics in the high-latitudes. This leads to a very large localized eastward GW drag reaching a maximum in the upper thermosphere as a consequence of enhanced molecular viscosity, thermal conduction, and ion drag. Overall, this study highlights that in studies of the thermosphere at equinox, GWs should be taken into account. 1. Yigit, E., A. D. Aylward, A.S. Medvedev (2008), J. Geophys. Res., 113, D19106, doi:10.1029/2008JD010135. 2. Yigit, E., A. S. Medvedev, A. D. Aylward, P. Hartogh, and M. J. Harris (2009), J. Geophys. Res., 114, D07101, doi:10.1029/2008JD011132.

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